1. Field of the Invention
The present invention relates to a diagnostic system for an internal combustion engine, and more particularly, to a diagnostic system for an internal combustion engine which is suitable for a device detecting an air-fuel ratio imbalance between cylinders or detecting an air-fuel ratio of a cylinder in a multi-cylinder internal combustion engine.
2. Description of Related Art
In recent years, Japanese Patent Application Publication No. 2013-142302 (JP 2013-142302 A) discloses a diagnostic system for an internal combustion engine that detects an air-fuel ratio or an air-fuel ratio imbalance between cylinders using an in-cylinder pressure sensor. In the diagnostic system according to the related art, an amount of fuel injected of a target cylinder is changed so that a combustion rate reaches a peak value. Information on the air-fuel ratio of the target cylinder is calculated on the basis of the change in the amount of fuel injected from the change start of the amount of fuel injected to the reaching of the peak value of the combustion rate.